The present invention relates to a flow-through flow meter having ultrasonic transducers for a respective transmission or respective reception of ultrasonic radiation. The transducers are mounted in association with a pipe such that the ultrasonic radiation passing through the flowing medium is analyzed. A difference between the ultrasonic radiation received in the flow direction and the ultrasonic radiation received counter to the flow direction may be utilized as a measure of the flow-through quantity and/or flow-through speed.
From state of the art publications such as "Flow, its Measurement and Control in Science and Industry", Vol. 1, Part 2; and "Flow Measuring Devices", pp. 897-915, Industry Society of America, Pittsburgh (1974) (both incorporated herein by reference), a number of flow-through flow meters operating with ultrasound are known. This latter comprehensive publication refers to many older printed publications. In particular, FIG. 3 (p. 905) and FIG. 4 (p. 907), illustrate arrangements comprising transmitting and receiving transducers whose radiation direction is directed obliquely to the axis of the pipe line, in the interior of which the flowing agent is to be measured with regard to speed and/or flowing quantity. All these embodiments are of such a type that the interior surface of the pipe wall exhibits an interference or fault due to a wedge-shaped depression or a wedge-shaped projection. Such disturbances or interferences of the pipe interior wall, however, are very undesirable, since, on the one hand, they cause disturbances in the flow profile, and hence in the flow resistance, and, on the other hand, they give rise to deposits at this location, whereby these deposits, moreover, also impair the propagation of the ultrasonic radiation.
In order to avoid such difficulties, constructions have been proposed which are illustrated in the above-cited publication in FIG. 6 (p. 908). An unaltered smooth pipe interior wall is present therein, and the transducers for transmission and reception are again mounted with the transmission- or receiving-direction, respectively, obliquely directed relative to the pipe axis. In accordance with one sample embodiment, a notch in the exterior wall of the pipe line is provided in which the respective transducer is mounted. This transducer must radiate, or receive, respectively, its ultrasonic radiation through the pipe wall, whereby, at the boundary surface between the pipe interior wall and the pipe interior volume, a refraction of the propagating ultrasonic radiation occurs which, moreover, is dependent upon changes in the refractive index of the medium flowing in the pipe line.
In another embodiment a transmission member for the ultrasonic radiation is inserted obliquely into the pipe wall, the actual transducer member being applied to the exterior end face of said transmission member. In the region of the interior wall of the pipe line, this transmission member has a surface which is a smooth continuation of the pipe interior wall. In the case of a transmission member of this type, the previously cited effect of radiation refraction takes place.
In an additional embodiment the transducer member is mounted on a coupling block which is secured externally to the pipe wall, whereby likewise the refraction occurs.
These various embodiments for the mounting of the transducer, which have already been known for quite some time, have, as already partially discussed, disadvantages of various types. The embodiments comprising transmission members (FIG. 6 of the publication) are, above all, also less sensitive, since the ultrasound passes through a considerable path distance in a medium, which is not influenced by the respective conditions in the flowing medium.